Supporters of Russian opposition leader Alexei Navalny are to stage a protest rally in Moscow with the defeated mayoral candidate demanding a recount of the vote because, he said, it was rigged.

The Kremlin-backed candidate, Sergei Sobyanin, won 51.3% of the vote. Navalny came second with 27%, elections officials said.

Navalny, a vocal critic of President Vladimir Putin, claimed that the winning result was artificially inflated to pass the 50% threshold and avoid a run-off.

"We don't recognise the results that have been announced. They are rigged," Navalny wrote on his blog.

Moscow authorities gave permission for him to organise a 2,500-strong demonstration in the streets of the capital.

The 37-year-lawyer, who has led large protests against Putin, said he wanted to sit down with Sobyanin to organise a recount.

The Moscow Election Commission denied any violations of the count.

Sobyanin, 55, a former Kremlin chief of staff and Moscow's incumbent mayor, described the vote as the "most honest and open election" in the capital's history.

The turnout fell to 32%. The Communist candidate, Ivan Melnikov, came third with 10.7%.

Although he never had a real chance of seizing the mayoral office Navalny's result was surprisingly strong for an opposition leader. He rose to prominence on an anti-corruption campaign and led some of the largest anti-Putin protests of the past few years.

According to election officials 632,697 Muscovites voted for him - a much higher figure than the turnout of his past street rallies.